Chromosomes and Inheritance

Transcription

1 Chromosomes and Inheritance Overview Number of instructional days: 14 (1 day = 50 minutes) Content to be learned Describe the structure of DNA as a way to demonstrate an understanding of the molecular basis for heredity. Diagram or model the relationship between chromosomes, genes, and DNA, including histones and nucleosomes. Distinguish the stages of mitosis and meiosis and how each contributes to the production of offspring with varying traits. Explain how alteration of the DNA sequence may produce new gene combinations that make little difference, enhance capabilities, or can be harmful to the organism. Understand how humans are affected by environmental factors, such as radiation or chemicals, and how such factors can cause gene mutations. Given a scenario, provide evidence that demonstrates how sexual reproduction results in a great variety of possible gene combinations. Essential questions What are the major components of DNA? How do they relate to the overall function of DNA? How does the molecular structure and packaging of DNA allow for its function in heredity and cell reproduction? How can alteration of chromosomes produce changes that could enhance capabilities or be harmful to the organism? Science processes to be integrated Predict, question, and hypothesize. Use tools and techniques to collect data. Represent, analyze, and interpret data. Use evidence to draw conclusions. Communicate understanding and ideas. Describe how structure affects function. Examine patterns of change. How can environmental factors cause gene mutations in humans? How can mitosis and meiosis each contribute to the production of offspring with varying traits? How does sexual reproduction (meiosis) result in a great variety of possible gene combinations and contribute to natural selection? Bristol-Warren, Little Compton, Portsmouth, Tiverton Public Schools, C-21

2 Chromosomes and Inheritance (14 days) Written Curriculum Grade-Span Expectations LS1 - All living organisms have identifiable structures and characteristics that allow for survival (organisms, populations, & species). LS1 (9-11) FAF+ POC -2 Explain or justify with evidence how the alteration of the DNA sequence may produce new gene combinations that make little difference, enhance capabilities, or can be harmful to the organism (e.g., selective breeding, genetic engineering, mutations). LS1 (9-11) 2 Students demonstrate an understanding of the molecular basis for heredity by 2a describing the DNA structure and relating the DNA sequence to the genetic code. LS1 (Ext) 2 Students demonstrate an understanding of the molecular basis for heredity by 2aa diagramming or modeling the relationship between chromosomes, genes and DNA, including histones and nucleosomes. LS3 - Groups of organisms show evidence of change over time (structures, behaviors, and biochemistry). LS3 (9-11) INQ POC-7 Given a scenario, provide evidence that demonstrates how sexual reproduction results in a great variety of possible gene combinations and contributes to natural selection (e.g., Darwin s finches, isolation of a species, Tay Sach s disease). LS3 (Ext) -7 Students demonstrate an understanding of Natural Selection/ evolution by 7aa distinguishing the stages of mitosis and meiosis and how each contributes to the production of offspring with varying traits LS 4 - Humans are similar to other species in many ways, and yet are unique among LS4 (9-11) NOS+INQ -9 Use evidence to make and support conclusions about the ways that humans or other organisms are affected by environmental factors or heredity (e.g., pathogens, diseases, medical advances, pollution, mutations). LS4 (9-11) 9 Students demonstrate an understanding of how humans are affected by environmental factors and/or heredity by 9a researching scientific information to explain how such things as radiation, chemicals, C-22 Bristol-Warren, Little Compton, Portsmouth, Tiverton Public Schools,

3 Chromosomes and Inheritance (14 days) Biology, Quarter 3, Unit 3.1 Clarifying the Standards Prior Learning In grades K 4, students learned that plants and animals need resources in order to reproduce. They labeled and used pictures to sequence the stages in life cycles of plants and/or animals. They observed changes and recorded data to scientifically draw and label the stages in a life cycle of a familiar plant or animal. In grades 5 6, students compared and contrasted asexual and sexual reproduction. They defined reproduction as a process through which organisms produce offspring. Students described reproduction as being essential for the continuation of a species. They also compared a variety of plant and animal life cycles. By grades 7 8, students furthered their understanding to include genetics. They described and gave examples of various types of asexual reproduction, such as binary fission and fragmentation. Students learned that sexual reproduction involves the combination of genetic material from two parents (e.g., egg/sperm). They described the major changes that occur over time in human development from single cell through embryonic development to new born. Students demonstrated this by identifying the stages of human embryonic development and describing the changes from one stage to the next. They compared and contrasted embryonic development in various life forms, such as humans and chickens. Students went on to compare the patterns of human development after birth to life stages in other species. Current Learning The level of instruction for this unit is both development and reinforcement of previous knowledge. Students demonstrate an understanding of the molecular basis for heredity by describing the structure of DNA. They accomplish this by diagramming or modeling the relationship between chromosomes, genes, and DNA, including histones and nucleosomes. Students go on to explain how alterations in chromosomes may cause changes that make little difference, enhance capabilities or can be harmful to the organism. After establishing this foundational knowledge of DNA structure and packaging, students distinguish the stages of mitosis and meiosis and how each contributes to the production of offspring with varying traits. Given a scenario, students provide evidence that demonstrates how sexual reproduction results in a great variety of possible gene combinations and contributes to natural selection. Students are expected to predict, question, and hypothesize possible outcomes of alteration to the DNA sequence and/or errors that could occur during mitosis/meiosis. They use tools and techniques to collect data regarding the stages of mitosis/meiosis. Students then represent, analyze, and interpret data, using evidence to draw conclusions about cycles (life cycle of cells and/or life cycle of multicellular organisms) in the natural world. All students should be able to communicate understanding and ideas. Early in this unit, students need to establish a clear understanding of the structure and packaging of DNA. Students apply this knowledge as they learn the cell cycle, in particular when they learn about DNA replication prior to mitosis and meiosis. During this unit, students should use their knowledge of DNA structure to understand DNA replication. This knowledge could then be applied to diagram or model a chromosome and to understand the relationship between DNA and chromosomes. As the unit progresses, students apply their knowledge of chromosomes to understanding the stages of mitosis and meiosis. Students could use microscopes with prepared slides of onion root tip or fish blastula Bristol-Warren, Little Compton, Portsmouth, Tiverton Public Schools, C-23

4 Chromosomes and Inheritance (14 days) or view images online or otherwise. In terms of mitosis, they should understand that without mutations the resulting daughter cells are identical (clones). This could be modeled using beads, pipe cleaners, etc. Students should learn about cancer and its relationship to the cell cycle. There are many different ways to introduce this, from viewing slides to investigating checkpoints in interphase. There are even several short videos available that help students to understand and make connections to real-life situations dealing with cancer. In terms of meiosis, the resulting daughter cells are not only haploid, but also contain a variety of gene combinations due to independent assortment and crossing over. This could also be modeled using the same materials. Students should also understand that the combination of two haploid cells (gametes) results in additional genetic variation making sexual reproduction a tremendous source of genetic variety with contributes to natural selection. To wrap up this unit, it might be helpful to allow students the opportunity to compare and contrast these two processes. This could be done in groups or independently though a product such as a poster, brochure, or other visual. During this unit, students might begin to understand the role of mutations in both mitosis and meiosis. This is a good opportunity to introduce the difference between basic DNA mutations (point, frameshift, etc.) and chromosomal mutations (nondisjunction, translocation, etc.). However, they will learn about mutations formally in Unit 3.2. At this time, students should learn how environmental factors, such as radiation or chemicals, could result in such mutations. Coming into high school, students had only a basic understanding of genetic material knowing that it is housed in the nucleus of a (eukaryotic) cell. They had an understanding of asexual versus sexual reproduction, but not at the molecular level. This is the main priority in high school understanding the nature of DNA and chromosomes and their role in reproduction. Future Learning In Unit 3.2, students will explore how DNA can be altered and how this affects genes and heredity. They will apply their knowledge of DNA structure to transcription and translation, looking more specifically at genes and their resulting proteins. Students will also apply this foundational knowledge to their future understanding of selective breeding, genetic engineering, and how genetic mutations occur. Students will rely on the knowledge from this unit throughout upcoming units. They will apply this foundational knowledge in their study of DNA to protein, genetics, and evolution. If students have not yet taken chemistry, they will use their knowledge of hydrogen bonds, covalent bonds, and biological molecules during the course. Additional Findings Although implied, it is not clearly stated that students must understand DNA replication. However, in order to understand the structure of a chromosome, they must understand that DNA has been copied and further that the cell cycle consists of more than just mitosis/meiosis (interphase and cytokinesis must be addressed). The same genetic information is copied in each cell of the new organism is shown as prior knowledge (to cell division / reproduction) on pp. 69, 71, 73, and 75 of Atlas of Science Literacy, Vol. I. Complex interactions among the different kinds of molecules in the cell cause distinct cycles of activities, such as growth and division (Atlas, Vol. 1, p. 73). Commonly held ideas about mutation often carry some misconceptions, such as the whole organism can mutate during their own lifetime. Although this is not inconceivable, it is not what is usually meant by mutation and is irrelevant to the origin of variation and heredity. (Atlas, Vol. 1, p. 70) C-24 Bristol-Warren, Little Compton, Portsmouth, Tiverton Public Schools,

5 Chromosomes and Inheritance (14 days) Biology, Quarter 3, Unit 3.1 There are several incorrect ideas among middle school and high school students regarding sexual reproduction. Students often equate sexual reproduction with copulation (e.g., many students consider in vitro fertilization an example of asexual reproduction). They do not understand that sexual reproduction is the fusion of specialized cells from two parents that does not necessarily require physical contact between the parents. Students often also assume that males of all species are larger and stronger than females and that the offspring produced by asexual reproduction are weaker than those produced by sexual reproduction. Students also assume that mutation and recessive have negative connotations. Using a modeling activity for meiosis that begins with a small set of chromosomes, introduces students to crossing over, and ends after fertilization can help students recognize that genes are discrete entities inherited from both parents. (The Biology Teacher s Handbook, 4th Edition, pp ) Students do not believe that plants are capable of sexual reproduction. Asexual reproduction was thought to be restricted to microorganisms. Students recognize that variation between species occurs, but regard it as a response to environmental conditions rather than due to inheritance. Lack of a precise concept distinguishing sexual reproduction from asexual reproduction appears to preclude an understanding of the origins of variation. Sexual reproduction is not recognized as a source of genetic variation within a population. There was a study done (with 15 year olds) in which only 1% of students gave an accurate explanation of variation, correctly involving reproduction. Several researchers have found that pupils, even before specific teaching, know the word gene and less frequently chromosome. However, pupils appear to understand little of the nature or function of genes and chromosomes, not appreciating that there is a chemical basis to inheritance. (Making Sense of Secondary Science, pp ) Bristol-Warren, Little Compton, Portsmouth, Tiverton Public Schools, C-25